1. Field of the Invention
The present invention relates to the field of cleaning of substrate surfaces, and more particularly to an apparatus and method for dry cleaning substrate surfaces using clusters formed from a process gas.
2. Description of the Related Art
Generally, as devices have become more highly integrated, the line width of semiconductor chips such as memory devices and central processing units has been also decreased. This high integration allows small sized particles which have not caused particular problems in the past to substantially affect the generation of failures in integrated circuits (ICs), and the size of particles which must be removed has become smaller and smaller. For instance, in 64 Megabit dynamic random access memory (DRAM), it is currently known that particles having diameter over 0.16 xcexcm may cause failures in ICs. Further increases in integration will require that particles having the size of approximately 0.10 xcexcm be removed. Also, it is well known that it is difficult to remove particles which are placed at a connection structure between wires having small line width or within contacts.
There is a spin scrubber method to remove the particles after forming an oxide or silicon film. The method sprays de-ionized water on a surface of a specimen while rotating the specimen. In order to increase the removing efficiency during the application of the above described skin scrubber method, a brushing process is additively performed, which brushes a surface of the specimen with a brushing unit being separated from the surface of the specimen.
The method has an advantage of effectively removing the particles without damaging the surface of the specimen but it is difficult to maintain an appropriate gap between the brush unit and the specimen. The method has also a drawback in that the structure of the specimen may be deformed or that a number of particles increases when the specimen has a fragile structure and is hydrophobic.
In order to resolve the drawback of the de-ionized water cleaning method which sprays de-ionized water on a rotating specimen wafer and is widely used in the cleaning process of semiconductor wafers, a cleaning method using an aerosol has been provided. This aerosol-using wafer cleaning method involves cooling a mixed gas of argon and nitrogen to near the liquification point of the mixed gas and spraying the cooled mixed gas through a nozzle into a low pressured chamber such that a part of the mixed gas forms solid particles. The solid particles as an aerosol in liquid and gas states collide with the specimen wafer, thereby removing the particles.
McDermott et al in U.S. Pat. No. 5,062,898, entitled SURFACE CLEANING USING A CRYOGENIC AEROSOL, discloses forming an aerosol containing argon solid particles by expanding a pressurized gaseous argon-containing stream, and removing particles or film on a surface of a specimen using the formed aerosol. Also, it is disclosed in the patent that a mixed gas containing argon gas is cooled to near the liquefaction point at a fixed pressure range of 20 psi to 680 psi prior to the expanding.
McDermott et al., in U.S. Pat. No. 5,294,261, entitled SURFACE CLEANING USING ARGON OR NITROGEN further describe the use of argon with nitrogen-containing solid particles as well as an aerosol containing argon-containing solid particles as cleaning source.
Tamai et al., in U.S. Pat. No. 5,512,106, entitled SURFACE CLEANING USING ARGON OR NITROGEN AEROSOL, introduced a concept and a nozzle implement as means for expanding gas. In the patent, Tamai et al. disclose previously cooling a mixture gas containing argon gas prior to supplying the mixture gas to the nozzle, and that the mixture gas supplied to the nozzle through the pre-cooling contains liquid drops of argon. The mixture gas containing previously cooled argon liquid drops is injected into an low pressured environment through the nozzle to thereby form a fluid containing argon solid drops which are created through adiabatic expansion and the fluid is then sprayed to a surface of a specimen for the cleaning.
Rose at al. disclose AEROSOL SURFACE PROCESSING in U.S. Pat. No. 5,931,721, in which they describe an apparatus for performing the cleaning method provided in the aforesaid U.S. Pat. No. 5,512,106.
Narayanswami et al., disclose AERODYNAMIC AEROSOL CHAMBER in U.S. Pat. No. 5,810,942, in which they claim a hydrodynamic structured chamber for spraying aerosol on a surface of aspecimen for the cleaning and allowing both of aerosol and objects such as particles as removed to be easily extracted.
Also, it was reported in Semiconductor International, August 1998, that ARIES, which is the trade name of a system for cleaning using a stream of cryogenic argon and nitrogen xe2x80x9ccrystalsxe2x80x9d, was applied to a cleaning process during device fabrication and thereby approximately 1-8% improvement in yield was achieved. The report shows that the yield improvement is greater when the equipment is applied after forming a high pressured oxide layer, after forming nitride layer, and after etching aluminum.
Separately from the goal of removing particles, various solvents had been developed in order to remove polymer which is formed on side walls of aluminum wire after the aluminum wire is deposited and then etched during patterning, and is being used in mass production of semiconductor devices. However, it is generally known that these solvents are ineffective in removing particles.
D. W. Moon et al. report in Journal of Vacuum Science and Technology A, Vol. 17(1) (January/February 1999), 150-154, the irradiation of ultraviolet rays onto a contaminated silicon wafer for the cleaning in an ambient of ozone. However, this method also is not effective in removing particles.
There is disclosed in U.S. Pat. No. 5,853,962, to Bowers, entitled PHOTORESIST AND REDEPOSITION REMOVAL USING CARBON DIOXIDE JET SPRAY, a method injecting a high pressured liquified CO2 through a nozzle, thereby transforming the liquified CO2 into soft solid CO2, and then spraying the solid CO2 on a surface of a specimen, thereby removing photoresist of organic material.
However, when this method is applied to silicon wafer processes, it is difficult to form high purity of CO2, thereby causing particles to be remained on the surface of the specimen during the evaporation of CO2 which has been compressed on the surface of the specimen. Since the remaining particles cause re-contamination of the specimen, it is anticipated that it is difficult to apply the method to silicon wafers which require high purity within near future.
U.S. Pat. No. 5,459,326, to Yamada, entitled METHOD FOR SURFACE TREATMENT WITH EXTRA-LOW-SPEED ION BEAM, describes a method injecting into a high pressurized vacuum chamber gas which passes through a nozzle without pre-cooling the gas which has passed through the nozzle, in which the method is characterized by using only adiabatic expansion due to a pressure difference between the gas pressure and the chamber pressure, differently from methods using aerosol, forming clusters through these processes, and accelerating these clusters from an accelerating terminal using electric field.
Deguchi et al., in U.S. Pat. No. 5,814,194, discloses SUBSTRATE SURFACE TREATMENT METHOD. This method is adapted for smoothing a surface of a diamond specimen formed by a chemical vapor deposition, in which cluster particles containing a plurality of molecules or atoms are prepared by a gas cluster forming method, are accelerated, and are sprayed on the diamond specimen. Although the clusters are accelerated with a sufficiently high voltage, since the clusters containing a few thousand molecules have a large mass while are ionized into a monovalent ion, an energy of the molecules contained in the cluster is smaller than that of molecule ions and the clusters are fragile as soon as they collide with the surface of the specimen. Thus, although sufficiently accelerated clusters are injected onto the surface of the specimen, the molecules contained in the cluster damages or stays at the surface of the specimen rather than they are deeply stuck at a depth from the surface of the specimen.
It is therefore an object of the present invention to provide an improved method and apparatus for cleaning a substrate surface.
A further object of the present invention to provide a method and an apparatus capable of removing particles or organic remnants without damaging the surface of the specimen.
A yet further object of the invention is to provide a method and apparatus capable of removing smaller particles from the surface.
A still further object of the invention is to provide a simpler and less expensive method and apparatus for cleaning a substrate surface.
It is another object of the present invention to remove particles or organic remnants without using ionized and accelerated clusters.
These and other objects and advantages are provided by the present invention, as will become more apparent with the following description.
According to one aspect of the present invention, there is provided a dry cleaning method which includes the steps of: forming a neutral cluster; and injecting the neutral cluster at a selected angle with respect to a surface of a specimen which is being cleaned.
The forming step includes the steps of: establishing the specimen in a chamber having a first pressure; supplying a cleaning gas having a second pressure into the chamber through a nozzle shaped as a sand glass of which a diameter decrease along a progress path of the cleaning gas to a first length of the sand glass and increases from the first length to a second length; and adiabatically expanding the cleaning gas injected from the nozzle using a pressure difference between the first pressure of the gas and the second pressure of the chamber.
It is desirable that the first pressure ranges from approximately 5 psig to approximately 140 psig and the second pressure ranges from approximately 200 mTorr to approximately 0.01 mTorr.
According to another aspect of the invention, there is provided a dry cleaning apparatus which comprises: a chamber in which a specimen having a surface which is being cleaned is established; and a nozzle established within the chamber, for injecting a neutral cluster at a selected angle with the respect to the surface of the specimen. The chamber includes: a chuck for holding the specimen; and means for reciprocating and rotating the chuck.
It is desirable that the nozzle is shaped as an hour glass of which the diameter decreases along a progress path of the cleaning gas to a first length of the hour glass and increases from the first length to a second length.